1. Field of the Invention
The invention relates to color electrostatographic document production machines, and more particularly to automatic adjustment of parameters influencing the output copy color balance, color fidelity, and tone reproduction of such machines.
2. Description of the Prior Art
In electrostatographic document production machines such as printers and copiers, image contrast, density, and color balance can be adjusted by changing certain process control parameters. Such parameters most frequently include primary voltage V.sub.0, exposure E.sub.0, and development station electrode bias voltage V.sub.b. Other process control parameters which are less frequently used, but which are effective to control the image contrast, density, and color balance include the concentration of toner in the developer mixture, and the image transfer potential.
Techniques exist for regulating electrostatographic machine process control parameters so as to compensate for long term variations in the electrostatographic process. The phrase "long term" pertains to variations which would affect many successive images, and includes variations caused by such things as changes in toner concentration, wear of the image transfer member, aging of the exposure lamp, and atmospheric conditions.
Prior art systems attempt to diminish the adverse effects of these variations using manual or automatic set-up systems, or a combination of both. In typical manual set-up systems, a skilled operator examines the output reproduction (copy or print) and the corresponding input and output density (D.sub.in -D.sub.out) curves for red, green, blue, and black. Based on experience with the equipment, the operator determines adjustments to process control parameters, such as initial voltage V.sub.0, exposure E.sub.0, and development bias V.sub.b. Several iterations of adjustment may be required to achieve acceptable color reproductions, in terms of color balance, color fidelity, and tone reproduction.
During set-up, a skilled operator will generally image a neutral density step tablet and adjust the process for hue neutrality of the reproduction. After achieving reasonable neutrality, the operator will adjust for good tone reproduction (i.e., good light-to-dark progression, contrast, and absence of abrupt density changes between density steps). Finally, the operator will check and adjust for neutrality again, all this in an iterative procedure until satisfied with the overall resultant reproduction quality.
U.S. Pat. No. 4,894,685, issued Jan. 16, 1990 to Shoji, discloses a method for setting color process control parameters by forming a plurality of different density patches in a non-transfer portion of a photoconductor. Process control parameters are set in accordance with the differences between the recorded densities and "ideal case" densities referred to herein as "aim" densities. U.S. Pat. No. 4,647,184, issued Mar. 3, 1987 to Russell et al., relates to a set-up mode wherein test patches of varying density are compared to stored values. The operating process control parameters of charge, developer bias, and exposure are adjusted in an iterative process until there is convergence along three separate points of a stored aim curve of the photoconductor response to exposure.
Neither patent provides for field adjustments of the values of the aim points. Nor is the operator given the option to revert to the original set-up if desired. Further, there is no provision for producing prints of the toned patches, or for conserving consumables by delaying a print until all iterations are finished.